Springs have long been used to support all of the vehicle parts above its wheel assembly to protect as much of the vehicle as possible, especially the occupants, from road shocks. (Hereinafter, “wheel assembly” will be used to refer to parts which provide support to the lower ends of the springs, such as the wheels, tires, axles, axle tubes, and control arms, and “suspended load” will be used to refer to all of the other parts supported by, and riding up and down on, the springs.) Most often such springs have been horizontally-disposed leaf springs and/or vertically-disposed helical springs composed of resilient metal. A helical spring is typically disposed between a point near the axle or control arm of a wheel at its lower end and some point on the suspended load at its upper, such as a frame rail. Typically the ends of the spring are circular and fit into upper and lower spring retainers, more typically shaped like and referred to as cups. (A shock absorber may be combined with the spring to dissipate the energy of vertical oscillations of the wheel assembly relative to the suspended load, such as the tubular type sometimes mounted along the axis of the spring or the scissors type mounted outside of the spring.)
When a helical spring like this is held more or less vertically and biased downwardly by the weight of the suspended load, more happens to the spring than mere shortening. If the spring is rigidly held at both ends, two forces come into play. One, torque is more or less uniformly applied to every element of the helix (that is, the solid metal of the coil is twisted). This is the source of the “springiness” of the spring. Secondly, the helix material is compressed in the helical direction (that is, along the helical path of the center of the solid coil). This second force occurs because when the spring is compressed, the distance between the fixed ends shortens. The first force manifests itself merely by the flights of the helix becoming closer together, as expected and as readily observed. The second force is less perceptible, however, and manifests itself as a slight uncoiling of the spring. If the ends of the spring are truly fixed so that they cannot turn tangentially relative to one another (that is, they cannot rotate relative to one another about the helical axis of the spring) the force attempting to uncoil the spring tries to push the ends horizontally relative to one another. This is the force that makes a spring “pop out” from between perfectly parallel compressing surfaces, and is of a magnitude comparable to the vertical compressive force.
In an automotive application, the springs simply rest in the spring cups and are held there by the weight of the vehicle. The substantial weight of the vehicle effectively holds the ends of the spring rigidly so that they cannot rotate relative to one another about the axis of the spring. This means that as a car bounces on a road, the springs not only compress vertically but also try to force the suspended load in a horizontal direction relative to the wheel assembly, and vice-versa. When a car is turning, these forces combine to magnify the tendency of the suspended load to sway centrifugally away from the wheel assembly. Ordinarily, other parts in the vehicle are supplied to restrain such motion, such as an anti-sway bar between the front wheels. Springs on opposite sides of the vehicle may be slanted toward each other as well to compensate for this effect.
In an ordinary driving situation, the orientation an elasticity of the springs is selected according to the shape and weight of the vehicle for optimum safety, handling, and comfort on normal roads at normal speeds and under normal loads, and need not be (and often cannot be) changed. In an auto racing environment, in contrast, the way the springs affect handling becomes critical, and means is provided to permit replacement and adjustment of the springs. For this purpose, a jackscrew is interposed between the upper spring cup and the suspended load (typically at the frame rail) to adjust the weight distribution of the car and change the way the car handles in different circumstances. Typically, the jackscrew is male threaded in mating relationship to a female threaded part fixed to the suspended load so that the suspended load can be raised or lowered by turning the jackscrew. (A square drive recess is typically provided in the top of the jackscrew to enable it to be turned with a socket wrench.)
Currently, racing teams are competing using a relatively large anti-sway bar and relatively soft springs. To obtain proper weight distribution on the static vehicle, and in consideration of predicted operating conditions, springs are under a considerable amount of pre-loaded compression. As a result, and in combination with the forces described above, the springs exact great pressures on the spring cups and jackscrew threads, rendering them practically immobile. Also, due to these conditions the spring will not consistently perform as initially rated, as some of the kinetic energy storage capacity of the spring is consumed by the distorting forces described above. A need has therefore been identified for a way to relieve the uncoiling force on automotive springs as it occurs, so that each spring can better perform its purposes of axial suspension of vehicle weight, compression under intermittent load, effective transfer of vehicle weight from wheel to wheel, and dampening of vertical/horizontal forces in proportional amounts to the other suspension components.